Component placement machine as well as a method for transporting printed circuit boards

ABSTRACT

A component placement machine with a frame and with a transport device for transporting printed circuit boards in an X-direction as well as a method for transporting printed circuit boards whereby the transport device comprises at least one transport beam extending in the X-direction. The transport beam can be driven in the X-direction in a reciprocating movement, whereby the transport device is provided with a clamping mechanism connected to the transport beam for clamping on to a lateral edge extending in the X-direction of the printed circuit boards to be transported. The device is further provided with a supporting mechanism connected to the frame for supporting two lateral edges on both sides of the printed circuit boards, whereby the clamping mechanism can be brought into an active clamping position such that the clamping mechanism is active during the movement of the transport beam in the positive X-direction and can be brought to a resting position during the return of the transport beam in the negative X-direction. While the clamping mechanism is in a resting position the printed circuit boards are supported by the supporting mechanism.

The invention relates to a component placement machine with a frame andwith a transport device for transporting printed circuit boards in anX-direction, which transport device comprises at least one transportbeam extending in the X-direction, which beam can be driven in theX-direction in a reciprocating movement.

The invention further relates to a method for transporting printedcircuit boards with respect to a frame by means of a transport beam inan X-direction whereby at least one printed circuit board is moved bymeans of the transport beam from an initial position in a positiveX-direction to a predetermined position, after which the transport beamis lowered with respect to the printed circuit board in a negativeZ-direction over a predetermined distance, the transport beam is movedin the negative X-direction to the initial position and the transportbeam is moved up again in the positive Z-direction over thepredetermined distance.

Such a machine as well as such a method are disclosed in U.S. Pat. No.5,680,699 in which printed circuit boards in the form of strip shapedsupports are being transported and provided with electronic components.The strip shaped support or foil is on one lateral edge provided withholes through which transport pins of a transport beam are beinginserted. The transport beam is further provided with a clampingmechanism which extends along the other lateral edge of the foil. Bymeans of the clamping mechanism the foil is tautened in an Y-directedextending perpendicular to the X-direction and lying in the plane of thefoil.

When the foil has been displaced in the X-direction over the desireddistance, the clamping means are being released, the transport pins arebeing lowered and the transport beam is displaced in a negativeX-direction whilst the foil is lying with its lower surface on asupporting plate forming part of the frame.

In view of the high accuracy with which components have to be placed itis desirable to transport the printed circuit board by means of clampingmeans. Furthermore no specific transport holes need to be provided inthe printed circuit board, so that more freedom in the design of theboard is obtained.

This machine is, however, not suitable for printed circuit boards whichare already provided with components on its lower surface.

It is therefore an object of the invention to provide a componentplacement machine in which the above mentioned disadvantage has beenovercome.

This object has been achieved by the component placement machineaccording to the invention in that the transport device is provided withclamping means connected to the transport beam for clamping in at leastone lateral edge extending in the X-direction of the printed circuitboards to be transported, and in that the device is further providedwith supporting means connected to the frame for supporting two lateraledges on both sides of the printed circuit boards, which clamping meanscan be brought into an active clamping position such that the clampingmeans are active during the movement of the transport beam in thepositive X-direction and can be brought in a rest position duringreturning of the transport beam in the negative X-direction, in whichrest position of the clamping means the printed circuit boards are beingsupported by the supporting means.

Because the printed circuit board in the rest position of the clampingmeans, is being supported on the two lateral edges by the supportingmeans, the components connected to the lower surface of the printedcircuit board do not form obstacles for the supporting means.

Furthermore the supporting means on which the printed circuit boardssimply rest, do not exert undesired forces on the printed circuitboards, due to which the boards might be moved. In this manner a goodposition accuracy is obtained.

An embodiment of the component placement machine according to theinvention is characterized in that the clamping means comprise a fixedjaw portion, which cooperates with an upper side of the printed circuitboard and a moveable jaw portion which is movable in a Z-direction tothe fixed jaw portion to cooperate with a lower side of the printedcircuit board and is movable away from the fixed jaw portion to releasethe printed circuit board.

Due to the movable jaw portion it is relatively easy to clamp a lateraledge of the printed circuit board. Furthermore by lowering the movablejaw portion with respect to the fixed jaw portion, the printed circuitboard, resting on the movable jaw portion is also lowered, whereby thelateral edges of the printed circuit board can easily be put on thesupporting means connected to the frame.

Another embodiment of the component placement machine according to theinvention is characterized in that the fixed jaw portion comprises anumber of clamping elements which extend in an X-direction one behindthe other.

The use of clamping elements with dimensions smaller than a dimension ofeach of the printed circuit boards will achieve that each of the printedcircuit boards will always be clamped in by at least two clampingelements. If the clamping element is spring loaded and comprises forexample a leaf spring, differences in thickness of the printed circuitboards will easily be taken into account.

Another preferred embodiment of the component placement machineaccording to the invention is characterized in that the transport devicecomprises a bed of supporting pins, movable simultaneously with themovable jaw portion.

The supporting pins support the printed circuit board during transportand are located against the lower surface of the printed circuit boardon locations where no components are present. Furthermore the supportpins prevent deflection of the printed circuit board.

By simultaneously moving the movable jaw portion as well as thesupporting pins, a good support for the printed circuit board isobtained both during the transport of the printed circuit board in thepositive X-direction as well as during the lowering of the printedcircuit board and placing it on the supporting means connected to theframe. It is also an object of the invention to provide a method fortransporting printed circuit boards whereby the transport beam can bereturned to its initial position relatively quickly.

This object is being achieved by the method according to the inventionin that the movement of the transport beam in the negative X-directionas well as the Z-direction is partly simultaneously.

If the transport beam is already start moving in the negativeX-direction before the transport beam has been displaced in the negativeZ-direction over the predetermined distance, a time reduction is beingobtained. The transport beam can be moved in the negative X-direction assoon as all the elements of the transport beam which might hit againstcomponents on the lower surface of the printed circuit board are loweredenough to avoid collision. If use is being made of supporting pins, thesupporting pins must be lower over safety distance which is larger thanthe height of the biggest component connected to the lower surface ofthe printed circuit board. This safety distance therefore depends on thespecific printed circuit board which is provided with components in thecomponent placement machine. The safety distance is therefore preferablyadjustable. In the same manner the transport beam can be moved in apositive Z-direction from the predetermined distance to the safetydistance as soon as the transport beam is near its initial position. Assoon as the transport beam is at its initial position in X-direction,the transport beam can be moved upwards and the supporting pins arebrought against the lower surface of the printed, circuit board.

The invention will now be explained in more detail below with referenceto the drawing, in which embodiments of the component placement machinesaccording to the invention are shown by way of example.

FIG. 1 shows a front view of a component placement machine according tothe invention,

FIG. 2 shows a schematic side view of the machine as shown in FIG. 1,

FIG. 3 shows a detailed part of the side view as shown in FIG. 2,

FIG. 4 shows several steps for transporting printed circuit boardaccording to the invention,

FIG. 5 shows a graph of the movement of the transport beam of themachine as shown in FIG. 1.

FIG. 1 shows a component placement machine 1 according to the inventionwhich is provided with a frame 2 in which a transport device 3 isaccommodated. The component placement machine 1 is further provided witha number of component placement units 4. Such units 4 are known forexample from the above mentioned U.S. Pat. No. 5,680,699. Printedcircuit boards 5 can be transported through the machine 1 by thetransport device 3. The transport device 3 can be indexed over a certaindistance in a positive X-direction by driven means (not shown),whereupon the transport device 3 can be moved back into its initial orstarting position in the negative X-direction after said distance hasbeen covered. The printed circuit boards, transported by means of thetransport device 3 are provided with components by the units 4.

FIGS. 2 and 3 show a side view of the component placement machine 1 andespecially the transport device 3. The transport device 3 comprises atransport beam 6 which comprises two plates 7, 8 extending parallel toeach other. The plate 7 is movable with respect to plate 8 in andopposite to the Z-direction. The plate 7 carries a plate 9 on whichsupporting pins 10 are mounted. On one lateral side the plate 7 isprovided with a metal sheet 11 extending perpendicular to the plate 7.An edge 12 of the metal sheet 11 lies on the same height as the ends ofthe supporting pins 10. The plate 8 of the transport beam 6 is providedon a lateral edge with a plate 13 extending parallel to the metal plate11. The plate 13 is slidable mounted with respect to a guiding strip 14,connected to the frame 2. As can be seen in FIG. 3 the plate 13 isthereto provided with a set of wheels 15 forming guiding means withrespect to the guiding strip 14. By means of slidable mounted plate 13,the guiding strip 14 will be positioned in Y- and Z-direction. By meansof slidably mounted plate 13 the whole transport beam 6 can be moved inand opposite to the X-direction.

The plate 13 is provided on a side remote from the plate 8 with a part15 extending parallel to the plate 8 and above the edge 12 of the plate11. The part 15 forms a first jaw portion cooperating with the edge 12forming a second jaw portion of clamping means. Between said jawportions 12, 15 the printed circuit board 5 can be clamped. The part 15is, as can be seen in FIGS. 3 and 4, provided with a number of clampingelements 16 which extend in an X-direction one behind the other and areconnected by means of leaf springs 17 to the part 15.

On a lateral side remote from the knife shaped thin plate 11, arelatively thin plate 25 is mounted on the plate 9 which plate 25extends to the same height as the ends of the supporting pins 10. Theplate 25 supports a components free lateral zone of for example 3 mm ofthe printed circuit board 5.

The guiding strip 14 is on a side directed to the part 15 provided witha ridge 18 forming part of supporting means for the printed circuitboard 5. The supporting means for the printed circuit board 5 comprisesfurthermore an element 19 which is movable in and opposite to theY-direction to be able to support printed circuit boards 5 withdifferent width. The element 19 is provided with a ridge 20 lying on thesame height as the ridge 18.

The element 19 is furthermore provided with a spring loaded element 26which presses the printed circuit board 5 against the plate 25. Duringtransport the printed circuit boards 5 slide along the spring loadedelement 26.

The operation of the machine will now be explained with reference toFIG. 4 in which several steps I-VI are shown for transporting a printedcircuit board 5. In step I three printed circuit boards 5 are located inthe machine 1 and are resting with their lateral edges on the ridges 18,20 of the supporting means. The plate 7 of the transport beam 6 as wellas the plate 11 connected thereto is located in a relatively lowposition whereby the edge 12 is located under the level of the ridges18, 20.

In step II the plate 7 of the transport beam 6 together with the plate11 and the supporting pins 10 has been moved in the positive Z-directionwhereby lateral edges 21 (see FIG. 3) of two boards 5 are clamped inbetween the edge 12 of the plate 11 and the clamping elements 16.

The lateral edges of the printed circuit board necessary for beingsupported and being clamped in need to be free from components. Thiscomponent-free lateral zone is for example 3 mm.

As can be seen in FIG. 4, each printed circuit board 5 is clamped in byseveral clamping elements 16, the length of which being smaller than thelongitudinal dimension of the printed circuit board. It is achievedthereby that each of the printed circuit boards will be satisfactorilybe clamped in by at least one clamping element in spite of possiblethickness differences among the printed circuit boards. As can befurther seen, in step II the printed circuit board 5 on the right sideis being removed from the machine 1, for example by means of an endlessbelt 22 as shown in FIG. 1.

In step III the transport beam 6 together with the clamped in circuitboards 5 is transported in X-direction. The transport in X-direction canbe stepwise so that each printed circuit board 5 will stop under eachcomponent placement unit 4 to provide it with components. Before acomponent is placed on the printed circuit board 5, the exact positionof the board 5 with respect to the component placement unit 4 can bedetermined by means of a camera mounted on the unit 4.

In step IV the transport beam 6 has reached a position in which aprinted circuit board 5 is located near the end of the transport device3. A new printed circuit board 5 can now be brought in by means of, forexample an endless belt 23 (see FIG. 1).

The transport beam 6 is provided near the left side with a stopper 27 towhich the new printed circuit board 5 transported by the endless belt 23will abut. As soon as the new board 5 is near the stopper 27, an opticalsensor 28 will detect it and send a signal to the driven means of theendless belt 23 to reduce its speed so that the board 5 will slowly abutagainst the stopper 27. The stopper can be displaced from the left sideto the right side in case that the machine 1 will be driven in theopposite direction. On the right side 29 an optical sensor 29 is alsomounted on the transport beam 6. By means of said optical sensor 29 itis possible to detect a printed circuit board 5 on the right side of thetransport beam 6. If said printed circuit board 5 has not yet beenremoved and is detected by the optical sensor 29 an upward movement ofthe transport beam 6 can be stopped to prevent damage to the machineand/or the printed circuit board.

As shown in step V the plate 7 together with the plate 11 and thetransport pins 10 is moved in negative Z-direction whereby the printedcircuit boards 5 will also move downwards until the lateral edges of theprinted circuit board 5 abut the ridges 18, 20 of the supporting meansand will rest thereon. Now the transport beam 6 can be moved in negativeX-direction until it has reached the initial position as shown in stepI. The cycle of transporting printed circuit boards 5 can now be startedagain.

In FIG. 5 a graph is shown in which the movement of the transport beam 6and especially the plate 7 and the metal plate 11 connected thereto isshown. First, the transport beam 6 is indexed in several steps S1, S2and S3 to transport the printed circuit boards 5. Then the plate 11 ismoved in negative Z-direction to a safety distance at level Zsafe onwhich level the supporting pins 10 are located below all components 24connected to the lower surface of the printed circuit board 5. As soonas the plate 11 and the supporting pins 10 has reached the level Zsafe,the transport beam 6 start moving in negative X-direction whilst theplate 11 continues moving in negative Z-direction until it has reachedthe level Zmin. Due to this combined movement, the time necessary forthe movement of the transport beam 6 back to the initial position isreduced. As soon as the transport beam 6 reaches it initial position,the plate 7 and the plate 11 are being moved upwards to the level Zsafe.When the transport beam 6 has reached its initial position, the plate 11is moved beyond the Zsafe level to the initial Z0-level on which theprinted circuit board 5 is supported by the transport pins 10 andclamped in between the edge 12 of the plate 11 and the spring loadedclamping elements 16. Also due to the combined movement in negative X-and positive Z-direction near the initial position of the transport beam6 a reduction of the time necessary for the return movement of thetransport beam 6 has been achieved.

The positive X-direction can be directed to the right side of themachine 1 as well as to the left side.

The predetermined position to which the transport beam 6 is indexed isprogrammable. Also the steps S1, S2 etc. are programmable.

It is also possible to clamp in the printed circuit boards 5 on bothlateral edges during transport.

1. A component placement machine comprising: a frame; a transport devicefor transporting printed circuit boards in an X-direction; at least onetransport beam that extends in the X-direction, whereby the beam can bedriven in the X-direction in a reciprocating movement; a clampingmechanism connected to the transport beam for clamping in at least onelateral edge that extends in the X-direction of the printed circuitboards to be transported; and a supporting mechanism connected to theframe for supporting two lateral edges on both sides of the printedcircuit boards, whereby the clamping mechanism is placed into an activeclamping position such that the clamping mechanism is active during themovement of the transport beam in the positive X-direction and is placedin a resting position during the returning of the transport beam in thenegative X-direction, such that while the clamping mechanism is at restthe printed circuit boards are supported by the supporting mechanism. 2.A component placement machine according to claim 1, wherein the clampingmechanism comprises: a fixed jaw portion, which cooperates with an upperside of the printed circuit board; and a moveable jaw portion, which ismovable in a Z-direction toward fixed jaw portion to cooperate with alower side of the printed circuit board and which is movable away fromthe fixed jaw portion to release the printed circuit board.
 3. Acomponent placement machine according to claim 2, wherein the fixed jawportion comprises a plurality of clamping elements that extend in anX-direction; each clamping element positioned behind the other.
 4. Acomponent placement machine according to claim 3, wherein each of theplurality of clamping elements comprises a leaf spring.
 5. A componentplacement machine according to claim 2, wherein the transport devicecomprises a bed of supporting pins, that are configured to movesimultaneously with the movable jaw portion.
 6. A component placementmachine according to claim 1, wherein the supporting mechanism comprisestwo ridges extending in the X-direction.
 7. A component placementmachine according to claim 6, wherein the distance between the ridges isadjustable.
 8. A method for transporting a printed circuit boardcomprising the steps of: moving a printed circuit board by means of atransport beam, from an initial position in a positive X-direction to apredetermined position; lowering the transport beam with respect to theprinted circuit board in a negative Z-direction over a predetermineddistance; moving the transport beam in the negative X-direction to theinitial position; and moving the transport beam in the positiveZ-direction over the predetermined distance whereby the movement of thetransport beam in the negative X-direction as well as the Z-directionoccurs simultaneously.
 9. A method for transporting a printed circuitboard according to claim 8, wherein the movement of the transport beamin the negative X-direction begins as soon as the transport beam hasbeen moved in the negative Z-direction over a safety distance but beforethe transport beam has been moved in the negative Z-direction over thepredetermined distance.
 10. A method for transporting a printed circuitboard according to claim 8, wherein the movement of the transport beamin the positive Z-direction begins before the transport beam is at theinitial position in the X-direction and wherein only after the transportbeam has reached the initial X-position is the transport beam moved froma safety distance to the initial position in Z-direction.
 11. A methodfor transporting a printed circuit board according to claim 9, whereinthe safety distance is adjustable.